Trained Marksman. Before you make a ranged attack with a ranged weapon with which you are proficient, you can choose to take a -5 penalty to the attack roll. If you do so and the attack hits, it deals +5 damage. AND you gain proficiency with firearms.

Keen Eye. Advantage on Perception checks that rely on sight.

Partially Deaf.  Disadvantage on hearing checks. 

Rage. On your turn you can enter a rage as a bonus action. You have advantage on Strength checks and Strength saving throws. When you make a melee weapon attack using Strength, you gain a +1 bonus to damage roll. You have resistance to bludgeoning, piercing, and slashing damage. You have advantage with melee weapon attacks, but attacks against you have advantage.
Your rage lasts for 1 minute. It ends early if you haven’t attacked a hostile creature since your last turn or taken damage since then. You can also end your rage on your turn as a bonus action. Entering this state brings back terrible memories of the civil war, and the war against the Comanches. (madness determined by DM).
You gain a level of exhaustion each time you use this...

The Equalizer. Gain +3 bonus to damage rolls if you are below half hit points. 

Unfinished Business. If you recover from death saving throws, you are not unconcious. You come back to the fray with 1 hit point.

Inspire (1/Day). You can spend 1 minute telling a story to inspire creatures other than itself. Any that can hear the story gain 1 temporary hit point. 

Haunted. You are haunted by your past as a soldier. You smoke regularly and drink like a fish. If you don't smoke your pipe or drink at least a cup of hard alcohol a day you will suffer severe symptoms. (determined by DM).
Although, the only thing that scares you is the monster you have inside of you. Immune to frightened condition.

Limp. Injured his leg from during battle, making moving more difficult. -10ft movement (subtracted).

Unarmed Attack. You can punch, kick, head-butt, or use a similar forceful blow and deal bludgeoning damage equal to 1 + STR modifier

Trained Combatant. If wielding a weapon you can roll a second attack with it and hit with the rifle butt, pistol handle, sword pommel etc for an extra Unarmed Attack.

Atonement. If an ally within 5ft would take an attack, you can take the attack instead if you manage to succeed on a Dexterity check that beats the attackers attack roll.